Apparatus for transferring wafer and ring

ABSTRACT

For wafer processing, wafers are transferred between a thermal treatment chamber and a thermal treatment installation. The treatment chamber has a top section and a bottom section between which the wafer is accommodated during treatment. The thermal treatment installation has a loading chamber having loading means and transport means. The wafer is place on a wafer support while in the loading chamber, wherein the wafer support is configured as a ring having support elements to support the wafer. The wafer support loaded with the wafer is inserted into the thermal treatment chamber so that the wafer and the wafer support are positioned between the top section and the bottom section. The wafer is individually processed in the thermal treatment chamber. After processing the wafer, the wafer support is removed from the thermal treatment chamber.

FIELD OF THE INVENTION

The present invention relates to a method of transferring a waferbetween a thermal treatment chamber and a thermal treatmentinstallation.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,162,047 discloses a thermal treatment installation whichcomprises a thermal treatment chamber, a “wafer boat”/rings assembly, aloading device and a transport device. With this arrangement the loadingdevice serves to place wafers in and to remove wafers from the assemblyand the transport device serves to place the assembly in and remove theassembly from the thermal treatment chamber.

The assembly consists of a frame to which a large number of rings arejoined equally spaced, with their flat sides positioned above oneanother. The rings are each provided with a recess, which is notspecified in more detail, in the inner edge, on which a wafer can beplaced by the loading device.

After loading a large number of wafers, the assembly is moved by thetransport device to the thermal treatment chamber to subject all wafers,located on the recesses, simultaneously to a treatment in which a heattreatment takes place.

In installations as disclosed in U.S. Pat. No. 5,162,047 the wafersremain in contact with the rings during the entire heat treatment.

During heat treatment of a substrate, for example a silicon wafer,plastic deformation of the wafer can occur. In the case of silicon attemperatures higher than 900–1000° C. the mechanical strength of thewafer decreases substantially and plastic deformation can occur moreeasily than at room temperature. The deformation of silicon wafersoccurs because crystal planes can shift over one another under theinfluence of stresses present or generated in the material. This isknown by the term “slip”. This slip can lead to warping of the wafersuch that this is detectable with the naked eye.

Two sources of stress which give rise to slip will be present in thematerial. Firstly, the force of gravity, which in the case ofhorizontally positioned wafers is exerted uniformly over the entiresurface thereof, in combination with the wafer support, which in generaltakes place at only a few points. This leads to local mechanicalstresses, in particular on and close to the support points, which arealso termed gravitational stresses.

Secondly, there is a temperature gradient over the wafer which leads toa non-uniform expansion of the wafer with corresponding mechanicalstresses, also referred to as thermal stresses. This temperaturegradient over the wafer occurs in particular on introducing it into areactor and removing it therefrom. In general the temperature in thereactor will be appreciable, for example 900–1000° C., in order toachieve an adequate throughput time. If the ambient temperature is roomtemperature, on introduction of the wafer into or removal of the waferfrom the reactor a substantial temperature gradient will be produced,with the resultant stresses. After all, the thermal capacity isrelatively low because of the limited thickness and the large radiatingsurface of the wafer.

In installations as disclosed in U.S. Pat. No. 5,162,047 the wafers arethus also subjected to a temperature difference during heating andcooling at those locations where there is contact with the ring, sincethe ring has a certain thermal capacity. So as not to allow temperaturedifferences during loading into and unloading from the thermal treatmentinstallation to become so large that mechanical stresses in the waferlead to plastic deformation, transport of the combination into and outof the thermal treatment chamber must always take place at a suitablespeed.

Moreover, the connection between the rings and the frame gives rise toan additional difference in thermal capacity in the rings which, as aresult of the positioning of the connection, can lead to local deviationof the temperature in the ring and the wafer, as a result of whichmechanical stresses can also be produced locally in the wafer duringheating/cooling. Local adverse deformation of the wafer can occur as aresult.

In some installations treatment is not carried out on a large number ofwafers at the same time, as in U.S. Pat. No. 5,162,047, but, for reasonsspecific to the treatment process, only one wafer is treated at a time.For such thermal treatment installations in which only a single wafer istreated per thermal treatment it is customary according to the prior artto place the wafer in, or remove the wafer from, the thermal treatmentchamber individually, that is to say directly with the aid of atransport mechanism and without an auxiliary support such as, forexample, a wafer ring.

SUMMARY OF THE INVENTION

The present invention relates in particular to contact-free treatment ofa wafer. For this treatment the wafer in a reactor is supporteduniformly over the entire surface by a gas stream, so that nogravitational stresses can arise during the treatment. The top sectionand bottom section of the reactor, between which the wafer isaccommodated, can be heated very uniformly so that no temperaturegradient of any significance is produced over the wafer during thetreatment. However, it has been found that during loading or unloadingof the wafer the abovementioned stresses can still occur, as a result ofwhich slip takes place. After all, according to the prior art the waferis picked up by a cold gripper for introduction and removal, high localtemperature gradients are produced close to the support points and slipoccurs. Likewise, an appreciable temperature gradient is produced overthe wafer as a whole. This gradient has two components: a linear and aradial component. The linear component arises because the wafer iswithdrawn from between the two hot reactor bodies (top section andbottom section) in a linear movement. The radial component arisesbecause the edge of the wafer is able to radiate its heat over a widerangle than the mid section of the wafer. The radial gradient inparticular leads to harmful stresses.

The aim of the present invention is further to restrict or completely topreclude the slip in a wafer during transport into and out of thethermal treatment chamber and in particular during the contact-freetreatment.

An aspect of the present invention involves a method of transferringwafers into and out of a thermal treatment chamber in a thermaltreatment installation. The treatment chamber has a top section and abottom section between which the wafer is accommodated during treatment.As illustrated in FIG. 12, the thermal treatment installation 100 has aloading chamber 120 in which one wafer 6 of a set of wafers is combinedwith a ring 1 in a wafer/ring combination. The loading chamber 120 hasloading means for placing the wafer 6 on a wafer support 1 and transportmeans for moving the wafer/ring combination. The wafer 6 is placed onthe wafer support 1 with the loading means while in the loading chamber120, wherein the wafer support 1 is configured as a ring having supportelements to support the wafer 6. The wafer support 1 loaded with thewafer 6 is inserted into the thermal treatment chamber 110 of thereactor 10 using the transport means so that the wafer 6 and the wafersupport 1 are positioned between the top section and the bottom sectionin the thermal treatment chamber 110. The wafer 6 is individuallyprocessed in the thermal treatment chamber 110. After processing thewafer 6, the wafer support 1 is removed from the thermal treatmentchamber 110.

It is pointed out that arranging a ring around a wafer in order torestrict the temperature gradient over the wafer is known per se. Theso-called “rapid thermal processing system” with which a wafer is heatedvery rapidly with the aid of lamps is described in U.S. Pat. No.4,468,259. With this system the wafer is mechanically supported and theradial temperature gradient in particular leads to slip because of heatloss at the edge of the wafer. This slip is appreciably reduced byarranging a ring which absorbs thermal radiation around the wafer holderwith a diameter somewhat larger than the diameter of the wafer. However,this ring is not used for transport of the wafer into and out of thereactor, so that the abovementioned stresses still arise duringloading/unloading. This also applies in the case of the ring arrangedaround a wafer as described in U.S. Pat. No. 5,334,257. Here again thethermal capacity of the edge region of the wafer is increased and theedge will heat up less rapidly and a less pronounced radial temperaturegradient will thus be produced over the wafer.

In U.S. Pat. No. 4,468,259 the ring is located in a fixed position inthe thermal treatment chamber. In U.S. Pat. No. 5,334,257 the rings arearranged in a wafer rack and the rings serve only as transport meanswhen transporting all wafers simultaneously.

The rings according to the invention can, of course, be handled by anyrobot known from the prior art.

The invention also relates to a thermal treatment installation/ringcombination, wherein said thermal treatment installation comprises atreatment chamber delimited by two sections located opposite oneanother, wherein at least one of said sections is provided with a gassupply for floating positioning of a wafer between said sections,wherein said ring is designed to be placed between said sections,wherein in the operating position the distance between said two sectionsat the location of said ring essentially corresponds to the thickness ofsaid ring and wherein at least three radial gas passages are arrangedbetween said ring and the section concerned. Using such a combination ofthermal treatment installation and ring it is possible accurately todetermine the horizontal position of a wafer in a floating waferreactor. In general, when positioning the wafer horizontally a gasstream will move towards the wafer both from the bottom and from the topof the reactor chamber in order to position said wafer accuratelybetween the top section and bottom section of the reactor. Forpositioning in the horizontal plane a ring which is provided withoutflow openings for said gas can be arranged around the wafer. It hasbeen found that if the wafer moves towards a particular edge of the ringthe outflow opening located in that position will be closed off to someextent, as a result of which a rise in the pressure of the gas occursbetween the ring and the related edge, as a result of which the ring ispushed back towards the centre again. This is promoted in that the otheropenings allow more gas through, as a result of which a lowering inpressure occurs at these locations. In this way, particularly stablepositioning is obtained and it is possible to work with a very smallwidth of the gap between wafer and ring, for example approximately 0.2mm. As a result of the use of such a ring the construction of thereactor walls, that is to say the top section and bottom section, can beappreciably simplified and can be made essentially flat. The passagethrough which the gas flows between the ring and the wall of the reactorcan be made either in the wall of said reactor or in the top or bottomof the ring or in both. Lateral positioning of the wafer in the reactoris provided with the aid of the constructions according to theinvention.

During introduction and removal of the wafer/ring combination the wafercan bear on support points on the ring. However, it is also possible toprovide a separate auxiliary element equipped with support pins whichextend through grooves or openings made in the reactor walls or in thetop or bottom of the ring as described above, the ring and the waferbearing on said support pins during movement. In a preferred variantsaid auxiliary element is likewise annular.

In a further preferred embodiment of this variant the support pins areprovided with internal channels which at one end open onto the contactsurface with the wafer and at the other end are in communication with aninternal channel in the auxiliary ring, which channel is connected tovacuum means in order to produce a vacuum in the channels. As a resultof the vacuum the wafer is pressed against the contact surface of thesupport pins with a greater force than just by the force of gravityexerted on the wafer and the wafer will shift less rapidly in thehorizontal plane during acceleration or retardation.

The invention also relates to a thermal wafer treatmentinstallation/ring combination comprising a thermal wafer treatmentinstallation having at least one receptacle for wafers, wherein saidreceptacle is constructed to receive a ring in such a way that the ringis removable and wherein each ring is designed to accommodate andsupport a wafer therein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference toillustrative embodiments shown in the drawing. In the drawing:

FIG. 1 shows a perspective view of a first embodiment of the ringaccording to the invention with a wafer removed therefrom;

FIG. 2 shows, diagrammatically, in cross-section, the ring according toFIG. 1 with wafer during introduction into a reactor;

FIG. 3 shows, diagrammatically, the ring with wafer according to FIG. 2during the treatment in the reactor;

FIGS. 4 a–c show, in cross-section, various variants of the ringaccording to the invention;

FIGS. 5 a,b show further variants provided with heating means;

FIG. 6 shows a plan view of a further embodiment of the ring accordingto the invention;

FIG. 7 shows a side view of the ring with wafer according to FIG. 6;

FIG. 8 shows a variant of FIGS. 6 and 7 with auxiliary ring;

FIG. 9 shows a side view of a construction according to FIG. 8introduced into a reactor;

FIG. 10 shows a variant of FIGS. 6 and 7 with auxiliary ring;

FIG. 11 shows a side view of a construction according to FIG. 8introduced into a reactor; and

FIG. 12 shows a plan view of a thermal treatment installation, accordingto preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

A first embodiment of the ring according to the invention is shown inperspective in FIG. 1 and is indicated in its entirety by 1. This ringconsists of a somewhat thicker outer edge 2 and a thinner inner edge 3.Three support pins 4 are provided. The ring 2 is provided with ahandling portion 5 for fixing to some sort of handling robot. A wafer isindicated by 6. The external diameter of the wafer 6 is somewhat smallerthan the internal diameter of inner edge 3, such that the wafer 6 bearson the support points 4 during transport thereof. Ring 1 is intended forsuch transport, as can be seen from FIG. 2. This figure shows theintroduction of the wafer 6 into a reactor 10 consisting of a topsection 11 and a bottom section 12 which are heated in some manner knownfrom the prior art. During introduction the wafer bears on the supportpins 4.

After the wafer has been introduced into the reactor 10 and the reactoris closed in some way, gas streams 13 and 14 are activated, as a resultof which the wafer conies away from the support pins 4 and starts tofloat and can be treated (FIG. 3). After treatment the gas streams 13and 14 are switched off and the wafer returns to the support pins 4 andis removed from the reactor. During introduction and removal the highheat gradient which is produced over the wafer is essentiallycompensated for by the presence of the ring 1. After all, as a result ofthe relatively high thermal capacity of the ring, more rapid cooling atthe edge of the wafer than in the centre thereof will be prevented. Thecooling characteristics or heating characteristics of the wafer duringtransport can be controlled by the selection of the material and controlof the wall thickness of the ring and the distance between the edge ofthe wafer and inner edge 3.

It must be understood that it is not necessary to allow the wafer torest on the support points during transport. In principle it is alsopossible to provide an arrangement by means of which the wafer is in thefloating state during transport. By this means it is guaranteed thatthere is no critical temperature transition at the support points.

As described above, the outer edge 2 of the ring 1 is made somewhatthicker. By this means mechanical strength is provided and the thermalcapacity increases. The differences between inner edge 2 and outer edge3 can comprise any construction conceivable in the state of the art. Afew examples are given in FIGS. 4 a–c.

Moreover, it is possible to supply heat from the ring during transportof the wafer. For this purpose heating elements 16 can be fitted, as isshown in FIG. 5. In the case of FIG. 5 a the material of the ring willconsist of a material that transmits radiation, such as quartz material.Consequently the distance from the heating element 16 to the inner ring3 does not constitute a problem. In the embodiment according to FIG. 5 bthe characteristics of the ring in respect of the transmission ofradiation are less important because the heating element is closer tothe wafer.

FIG. 6 shows a plan view of a further variant of the ring according tothe invention. This ring is indicated in its entirety by 21. The supportpins are indicated by 24. In contrast to the rings described above,radial gas passages are present, which are indicated by 22. In this casethese passages are grooves. FIG. 7 shows the various features incross-section during operation. It can be seen that gas stream 14 whichholds the wafer in the middle between the top section 11 and the bottomsection 12 is deflected and moves away in the radial direction over thewafer. However, the gases are only able to escape from the environmentof the wafer through the grooves 22. As a result of using the ring thex-y position of the wafer is accurately determined. After all, if thewafer 6 moves towards one of the grooves 22 the somewhat obstructingeffect of the wafer will mean that less gas can be discharged at thatlocation. As a result the pressure rises at that location and the waferwill move back.

A variant is shown in FIG. 8, the ring 31 shown in this figure not beingprovided with support points. A further ring 41 is arranged around ring31 and this ring is provided with support pins 34 which extend throughthe gas discharge grooves 32 which have been made in the bottom section12 of the reactor. FIG. 9 shows a cross-section of this variant,introduced into a reactor.

A variant is shown in FIG. 10, the ring 31 in this figure not beingprovided with support points. A further ring 51 is arranged around ring31 and this ring is provided with support pins 54 which extend throughthe gas discharge grooves 32 which have been made in the bottom section12 of the reactor. The support pins 54 are provided with internalchannels 56 which at one end open onto the contact surface 57 with thewafer and at the other end are in communication with an internal channelin the auxiliary ring 51, which is connected via communication passage55 to vacuum means (not shown) in order to produce a vacuum in thechannels. As a result of the vacuum the wafer is pressed against thecontact surface of the support pins with a greater force than just bythe force of gravity which is exerted on the wafer and the wafer willshift less rapidly in the horizontal plane on acceleration orretardation. FIG. 11 shows a cross-section of this variant, introducedinto a reactor.

Using the construction described in FIGS. 6–9, the top and bottomsection of the reactor, that is to say sections 11 and 12, can beproduced in a particularly simple manner. In this embodiment radialpositioning is achieved with the aid of the ring 21, 31. With thisarrangement the boundary surface of the top section 11 and bottomsection 12 with the reactor chamber can be essentially flat, a fewgrooves having been milled therein.

Those skilled in the art will understand from the large number ofvariants that have been described above that further developments arepossible without going beyond the scope of the present invention asdescribed in the appended claims.

1. A thermal treatment installation/ring combination comprising aloading chamber, loading means, transport means and a thermal treatmentchamber for carrying out a thermal treatment, said thermal treatmentchamber comprising a top section and a bottom section located oppositeto each other and between which a wafer can be accommodated for carryingout a thermal treatment, said transport means being equipped to movewafer/ring combinations from the loading chamber into the thermaltreatment chamber and vice versa, wherein said thermal treatment chamberis configured to carry out a thermal treatment on one wafer at a time,said transport means being equipped to move individual wafer/ringcombinations from the loading chamber and insert said individualwafer/ring combination into the thermal treatment chamber and viceversa, wherein the thermal treatment chamber is configured toaccommodate said ring surrounding the wafer and to hold the wafercontact-free in a floating state during the treatment, wherein aseparation between said top and bottom sections at a location of thering during the thermal treatment essentially corresponds to a thicknessof said ring.
 2. The thermal treatment/ring combination of claim 1,wherein said top section and bottom section are provided with heatingmeans.
 3. The thermal treatment installation/ring combination of claim1, wherein an internal diameter of an inner edge of the ring is largerthan an external diameter of the wafer.
 4. The thermal treatmentinstallation/ring combination of claim 1, wherein the ring is configuredto support said wafer at least during transfer.
 5. The thermal treatmentinstallation/ring combination of claim 4, wherein the ring ismechanically joined to the transport means.
 6. The thermal treatmentinstallation/ring combination of claim 4, wherein the treatment chamberis configured to accommodate an auxiliary element for supporting thering and the wafer at least during transfer.
 7. The thermal treatmentinstallation/ring combination of claim 6, wherein said auxiliary elementis mechanically joined to the transport means.
 8. The thermal treatmentinstallation/ring combination of claim 6, wherein said ring is providedwith heating means wherein the heating means are provided with the ring.9. A thermal treatment installation/ring combination comprising aloading chamber, wherein a wafer and a ring are combined to form awafer/ring combination, and a thermal treatment chamber for carrying outa thermal treatment, said thermal treatment chamber comprising a topsection and a bottom section located opposite to each other and betweenwhich the wafer can be accommodated for carrying out a thermaltreatment, wherein said thermal treatment chamber is configured to carryout a thermal treatment on one wafer at a time, wherein the thermaltreatment chamber is configured to accommodate said ring surrounding thewafer with a distance between said top and bottom sections at a locationof the ring during the thermal treatment essentially corresponding to athickness of said ring and where in the ring is configured to surroundthe wafer within the thermal treatment chamber and within the loadingchamber, wherein said installation/ring combination is configured andoperable to move the wafer/ring combination from the loading chamberinto the thermal treatment chamber and vice versa.